3 How does it work?

The source-me/haskell-env file exports PATH so that the ghc you chose earlier and the libraries are found by cabal.
Nix specific ghc(-*) wrappers are used to accomplish this.

4 On which OS Hack-Nix be used?

The set of tools is based on Nix, which performs best on any Linux.
It can be installed on Cygwin but I haven't tested this at all.
Nix installs into /nix and puts packages into /nix/store by default.
You can make it live within $HOME only as well.

5 HOWTO

Install nix. Please read the documentation found on the project homepage. If you've trouble join #nixos on freenode or join the mailinglist.

6 HOWTO uninstall a package

Brief: nix behaves like a memory manager. You run the garbage collector and all packages which are no longer referenced by any environment are removed automatically for you.

7 required quota

I haven't tested yet. Nix by default installs everything from scratch including glibc etc. There are solutions to make it work with libraries which are present on your system. However I haven't tried it because I'm running Nixos myself.

8 HOWTO make Hack-Nix know about my package ?

$ cd projectdir; hack-nix --to-nix

This will create a dist/name.nix file.
You can add this to your ~/nixpkgs/config.nix file.
Alternative: Tell hack-nix about additional packages in a configuration file. See mergeWith example above.

9 I've got a question

The purpose of this wiki page is telling you about the existence of this package rather than providing all details.
This is work in progress. Up to date information can be found in the README file.
I'm pretty sure I've missed important things you're interested in.
Join irc on freenode and contact me (MarcWeber).
I'm going to improve documentation ASAP.
Of course I want you to participate in this project :-)

10 How does it compare to cabal install ?

The solver is written in the Nix language (right now).
So it is slower. The advantages are that it optionally creates tag files for you. You never have to think about which packages to upgrade and about its consequences. You create a unique setup for project you're working on and that's it. If one package requires parsec-2 and another requires parsec-3 that's no problem. You never uninstall packages. You run the garbage collector once a month or so. Nix will install C library dependencies such as readline or postgresql automatically. cabal install is faster because it doesn't even compile Setup.hs each time. Nix starts a new build job for each dependency.
Nix supports concurrent builds. Hack-Nix will never replace cabal install.
It is an optional tool written for maintainers who have to handle multiple setups.